Binder cache for isUserUnlocked().

Bug: 140788621

Test: A special build that puts the PropertyInvalidatedCache in
verification mode was loaded on the device.  Then one iteration of MPTS
was executed.  No cache inconsistencies were found and no SELinux
violations (associated with the binder cache) were found.  The number of
cache misses was approximately 10% of the total binder calls.  All
binder calls went through the cache.  Added a new user and later deleted
the same user; verified that caches were invalidated as expected and no
errors were detected by the PropertyInvalidatedCache verification mode.

Passed the CtsMultiUserHostTestCases test.

Change-Id: I32e3e39768e288101c82b02e63a7eb20d5ed7f93